1. Field of Invention
The present invention relates to blast initiation devices. More specifically, the present invention relates to a detonator device having at least one signal transmission surface for communication of pressure impulse to neighbouring transmission lines or the like, in a detonator assembly or blasting system.
2. Description of Related Art
Concern about the versatility and precision of blasting systems has been the focus of the explosives industry for decades. Current blasting practices widely employ low brisance transmission lines as a non-electrical means of transmitting blasting signals to target detonators for initiating explosive columns in a precise and reliable manner.
Modern non-electric blasting systems typically comprise a series of shock tubes or signal transmission lines positioned in contact with a donor detonator within a connection block or the like. Transmission lines, or shock tubes as they are more commonly known, generally consist of a hollow tube housing a gas, and having an inner lining comprising a reactive material. The reactive material typically comprises aluminum powder and HMX explosive powder. These shock tubes are used to conduct an initiation impulse to the target detonators at remote locations within a blasting arrangement. Upon initiation, the pressure of an incoming impulse causes the wall of the shock tube to collapse, pressurizing and subsequently heating the gas within the tube and igniting the reactive lining.
A first detonator is generally initiated via an initiation shock tube to begin a chain of initiation steps within a blasting system. The pressure impulse generated by this first detonator is subsequently transmitted by neighbouring shock tubes to remote target detonators throughout the blasting system. Since the success of the ultimate blast or blasts is dependent on the reliability and timing of a pressure impulse arriving at the desired blast location(s), it is critical that all of the components of the blasting system are correctly and completely initiated. Upon initiation, the strength of the propagating pressure impulse is constant and independent of the mode of initiation and signal transmission line length. The propagation of such an impulse is therefore limited by the obstacles it encounters along a transmission pathway.
The prior art has largely focused on improving the precision and control of detonator initiation. In particular, the prior art teaches an extensive variety of detonator devices including timing control components for providing constant and stable ignition stimuli. The prior art also includes an abundance of connector components for use in blasting systems for precisely controlling the positioning of shock tubes with respect to detonators in blasting systems. These efforts have come a long way in improving the safety and reliability of detonator assemblies. However, given the nature of explosive compositions and devices, there is always room for improvement to the safety of the blasting systems employed worldwide.
European Patent No. 0 439 955 discloses a delay detonator having a transition element for providing a stable ignition signal to the delay train element of the detonator. According to this invention, a transition element separates the delay train element from the ignition source. This transition element comprises a material which, when ignited by an ignition signal, develops a substantially constant intensity for igniting the delay train element. As a result, this transition element stabilizes an ignition signal prior to igniting the delay train element of the detonator. More specifically, the delay time interval is dependent upon the intensity of the signal by which it is ignited. Accordingly, by providing a transition element of a suitable reactable material, the typical variable burn rate of an ignition signal can be transformed into a stable, quasi-steady state combustion rate for the controlled ignition of the delay train element. The time internal of the delay train element is therefore more precisely performed.
The detonator of this invention comprises of a typical tubular casing having a receiving end and a firing end. The exterior surface of the firing end of this detonator is shown to have a rounded shape As with most conventional detonator casings, the firing end of this detonator may be flat, rounded or otherwise shaped for convenience within a blasting system. An explosive composition is positioned within the tubular casing at a location most proximate to the firing end. The remaining components of the detonator are sequentially received through the receiving end according to their required role in the ultimate ignition of the explosive composition. The delay train element ignites the explosive composition contained at the firing end of the detonator. As a result, the delay train element must be positioned within the tubular casing of the detonator to contact the explosive composition. The explosive composition of this detonator includes both a primary charge and a base charge.
A detonation impulse initiated by a detonator of this type would naturally propagate from a point of initiation as a growing sphere. However, with the explosive composition confined to only one side of the initiation point, the propagating impulse will be concentrated in that direction. Further, heavy confining jackets may be provided within the tubular casing to position the delay train element, and subsequently confine the explosive composition. In this manner, the detonation impulse will be encouraged to propagate in a hemispherical fashion toward the firing end of the detonator.
As a result of the volume of explosive composition required by the detonator of EP 0 439 955, the delay train element is positioned a distance from the firing end which is substantially greater than the radius of the detonator. Accordingly, a propagating spherical or substantially hemispherical impulse will impact on the wall of the firing end at various rates.
U.S. Pat. No. 5,703,319 to J. E. Fritz et al. discloses a detonator assembly comprising a conventional flat end detonator and a connector block adaptable to receive six shock tubes. The connector block includes a rounded slot proximate a location for receiving the firing end of a detonator. According to this invention, a plurality of shock tubes can be receive into the rounded slot of the connector and extend in a direction perpendicular to the detonator. The rounded slot positions the plurality of shock tubes in fixed positions with respect to the firing end of the detonator.
When six shock tubes are received into the rounded slot of the connector, the two middle shock tubes are caused to shift away from the firing end of the detonator. This allows the next two shock tubes to be positioned closer to the centerline of the detonator. As a result, the positioning of the shock tubes of the detonator assembly of this invention is not spatially uniform and as a result, the shock tubes are not positioned to receive a uniform pressure impulse. As a result, the energy transfer efficiency to each shock tube will be variable.
U.S. Pat. No. 5,204,492 to Jacob et al. teaches of a detonator assembly comprising a low strength detonator containing low brisance primary explosives such as lead azide or lead styphate or compositions thereof, and a high confinement connection block. According to the invention of this patent, an assembly is provided which increases confinement of a plurality of signal transmission lines and facilitates the transfer of a pressure impulse upon detonation, while eliminating noise and shrapnel.
The connector block designs of this invention, increase the confinement of a plurality signal transmission tubes, thereby improving the energy transfer from the detonator to the lines, and subsequently reducing the amount of explosive composition required to obtain complete initiation. However, this reference does not provide for the uniform transmission of a pressure impulse from the firing end of a detonator to all signal transmission lines held in signal communication therewith.
Published PCT patent application WO 99/46221 to J. Capers discloses a detonator assembly which includes a detonator containing an explosive charge in a section of reduced diameter and a compatible connector block. According to this invention, two series of four shock tubes can be positioned adjacent the explosive section of the detonator at an orthogonal direction to the axis of the detonator body to receive an initiation impulse upon detonation. The spatial relationship of each shock tube with the explosive section of the detonator is the same, and initiation failures are thereby reduced. Although this arrangement is an improvement over the teachings of U.S. Pat. No. 5,703,319, the manufacture of such a detonator assembly is both complicated and expensive. In addition, the shock tubes of this arrangement are generally subjected to a lower pressure impulse generated from the sided of the explosive section of the detonator. Specifically, the pressure impulse generated by the explosive section of the detonator on detonation propagates in a direction parallel to the orientation of the explosive section and tangential to the walls of the shock tubes. Accordingly, the neighbouring shock tubes of this invention are not positioned to receive the maximum pressure impulse generated by the detonator. As a result, the energy transfer of this invention is sub-optimal. Consequently, the energy of the explosive composition has to be increased by the use of high brisance compositions such as PETN, which results in the increased production of residual noise and shrapnel.
Despite previous efforts to optimize detonators and detonator assemblies to improve the reliability and safety of blasting practices, limitations in these systems remain prevalent. As a result, there is a continued need for a detonator device which can reliably initiate a plurality of conventional signal transmission lines, under a variety of environmental conditions, while producing minimal amounts of noise and shrapnel.
It is an object of the present invention to provide a detonator device which reliably initiates a plurality of conventional signal transmission lines, under a variety of environmental conditions, while limiting the amount of residual noise and shrapnel.
It is another object of the present invention to provide a detonator device which uniformly accommodates a plurality of signal transmission lines for impulse transmission in a detonator assembly. The ability of the present invention to accommodate a plurality of signal transmission lines in a uniform impulse transmission arrangement facilitates the reliable transmission of a pressure impulse thereto.
It is a further object of the present invention to provide a detonator device with a contact wall for contacting a plurality of signal transmission for pressure impulse transmission, which is shaped to substantially correspond with the shape of a pressure impulse front generated therein.
It is a further object of the present invention to provide a detonator device capable of providing a substantially uniform pressure impulse to a plurality of signal transmission lines in impulse transmission contact therewith.
Another object of the present invention is to provide a detonator device and assembly for simultaneously initiating a plurality of signal transmission lines with a pressure impulse.
Yet another object of the present invention is to provide a detonator device and assembly adaptable to reliably initiate at least six signal transmission lines with a uniform pressure impulse.
According to one aspect of the invention, there is provided a detonator for initiating a plurality of signal transmission lines with a pressure impulse, comprising a detonator casing having a signal receiving end and a firing end, said firing end having a wall of substantially uniform thickness provided with a convex outer surface for contacting a plurality of signal transmission lines and a concave inner surface, said concave inner surface defining an inner region for holding an explosive composition, an explosive composition confined within said inner region; and means for conveying a firing signal received at said firing end to said explosive composition to initiate detonation of said explosive composition.
According to another aspect of the present invention, there is provided a detonator assembly for initiating a plurality of signal transmission lines with a pressure impulse, said detonator assembly comprising a detonator having a signal receiving end and a firing end, said firing end having a wall of substantially uniform thickness provided with a convex outer surface for contacting a plurality of signal transmission lines and a concave inner surface, said concave inner surface defining an inner region for holding an explosive composition, an explosive composition confined within said inner region, and means for conveying a firing signal received at said firing end to said explosive composition to initiate detonation of said explosive composition; and a connector element for receiving said detonator and said plurality of signal transmission lines in impulse transmission contact, said connector element comprising a conduit having opposing open ends for receiving said detonator, and a confining wall extending from one of said opposing ends to define a transverse slot for receiving said plurality of transmission lines there through; wherein when said detonator is positioned within said conduit said convex outer surface extends into said transverse slot to contact said plurality of signal transmission lines.
In accordance with yet another aspect of the present invention there is provided a connector element for connecting a detonator having an outer convex surface with a plurality of signal transmission lines, for transmission of a pressure impulse from said concave outer surface to said plurality of signal transmission lines, said connector element comprising a conduit extending through a body portion of said connector element; said conduit having opposing open ends; and a confining wall extending from one of said opposing ends and shaped to define a substantially rounded transverse slot; said transverse slot adapted to receive said plurality of signal transmission lines; and said conduit adapted to receive said detonator such that said outer convex surface of said detonator extends into said transverse slot to contact said plurality of signal transmission lines, wherein when said outer convex surface is positioned in contact with said plurality of signal transmission lines within said transverse slot, each of said plurality of signal transmission lines is uniformly positioned to receive a pressure impulse from said detonator.
By the term xe2x80x9cuniform pressure impulsexe2x80x9d we mean a pressure impulse having a substantially uniform strength and duration sufficient to reliably initiate a required number of signal transmission lines held in signal transmission contact with the detonator device of the present invention. For the purpose of the present invention, a pressure impulse will be sufficiently uniform when a pressure impulse is directed to impact on each point on an impulse transmission surface of the detonator of the present invention from a direction at an angle of 90xc2x120 degrees to a tangent at each point thereon.
In accordance with a preferred aspect of the present invention, a truly uniform pressure impulse will be provided when the impulse transmission surface of the detonator device is shaped to correspond with the shape of a propagating pressure impulse front, and a uniformly confined explosive composition is initiated at a central initiation point equally distanced from all locations on the impulse transmission surface. In this case, a pressure impulse front will impact on all locations along the correspondingly shaped impulse transmission surface at a normal angle of incidence and simultaneously initiate all signal transmission lines in contact therewith. In this manner, maximum energy transfer efficiency will occur.
By the term xe2x80x9cimpulse transmission surfacexe2x80x9d we mean a wall of the firing end of a detonator of the present invention, which transmits a pressure impulse from the detonator to a plurality of signal transmission lines in contact therewith. This wall or impulse transmission surface is substantially uniform in shape and thickness, and includes correspondingly shaped exterior and interior surfaces. The interior and exterior surfaces of the impulse transmission surface cooperate to transmit a substantially uniform pressure impulse to all signal transmission lines in contact with the impulse transmission surface. The impulse transmission surface of the present invention may be any suitable shape which substantially corresponds to the shape of a pressure impulse front generated by the detonator device on which it is located. By providing a detonator device with an impulse transmission surface shaped to correspond with the shape of a pressure impulse front impacting thereon, the uniformity of the propagating impulse can be substantially maintained. Accordingly, a substantially uniform pressure impulse can be transmitted from the detonator device of the present invention to a plurality of signal transmission lines in contact with the impulse transmission surface thereof.
The present invention provides a detonator device capable of transmitting a uniform pressure impulse to all location on an impulse transmission surface. When a pressure impulse impacts on the impulse transmission surface of the detonator of the present invention, at an angle of incidence which is xc2x120 degrees from normal to a tangent to each point thereon, a sufficient degree of energy transfer will occur at each point to reliably initiate a signal transmission line in contact therewith. Accordingly, the present invention is adaptable to generate a uniform pressure impulse of a suitable strength and duration to reliably initiate a predetermined plurality of signal transmission lines in contact therewith. In other words, the present invention is construct to provide a uniform pressure impulse to a required plurality of signal transmission lines. Further, the present invention is capable of reliably initiating a plurality of signal transmission lines under harsh environmental conditions.
The impulse transmission surface of the present invention is preferably shaped such that each of a plurality of signal transmission lines can contact an equal portion thereof. Further, according to an aspect of the present invention a uniform explosive composition is confined to a region of the detonator device defined by an interior surface of the impulse transmission surface, such that each point on the impulse transmission surface is proximate an equal amount of an explosive composition of sufficient strength to reliably initiate an impulse transmission line in contact with that point, upon detonation.
It is known in the art, that when an explosive composition is initiated at a central point within the firing end of the detonator of the present invention, a propagating pressure impulse will travel in all directions from the point of initiation, where sufficient explosive composition is provided. The impulse transmission surface of the present invention is preferably constructed to correspond to the shape of a detonation or pressure impulse front arriving at the location of the impulse transmission surface. By further confining a uniform amount of an explosive composition in contact with an interior surface of the impulse transmission surface, a uniform pressure impulse can be transmitted through the explosive composition, from a central initiation point, to arrive at the impulse transmission surface. The shaping of the impulse transmission surface to conform with the shape of the pressure impulse front, will facilitate transmission of a uniform pressure impulse to a plurality of signal transmission lines in contact therewith.
In accordance with a preferred embodiment of the present invention, a detonator is provided with an impulse transmission surface that is hemispherical about a central initiation point, such that each point on the impulse transmission surface is an equal distance from the central initiation point within the firing end of the detonator. An explosive composition is also uniformly confined between an interior surface of the impulse transmission surface and the central initiation point. According to this embodiment of the present invention, a normal pressure impulse can impact at all points on the impulse transmission surface and simultaneously initiate the plurality of signal transmission lines in contact therewith.
The impulse transmission surface of the present invention preferably includes a convex outer surface capable of uniformly contacting a plurality of signal transmission lines at equal distances from an initiation point within the firing end of a detonator.
Where the detonator device of the present invention is employed in a detonator assembly, a plurality of signal transmission lines can be uniformly positioned in signal transmission contact with the signal transmission surface thereof. Accordingly, the signal transmission lines are positioned to receive a uniform pressure impulse.
In a preferred embodiment of the present invention, a detonator assembly is provided for reliably initiating at least six signal transmission lines with a uniform pressure impulse.
The present invention achieves reliable initiation of a plurality of signal transmission lines with minimal production of residual noise and shrapnel.
Further, the detonator assembly of the present invention reliably initiates a plurality of signal transmission lines, under extremely cold and harsh environmental conditions.